Liquid electro-photographic (LEP) printing involves digital printing using electro-ink, which includes small color particles suspended in imaging oil that can be attracted or repelled to a photoconductive sheet (photo imaging plate) by causing a voltage differential on that sheet.
The first stage of LEP digital printing in such LEP printers involves selective charging of the surface of the Photo Imaging Plate (PIP) using its photo-induced electric conductivity and a laser beam. Next, charged liquid ink is applied to the surface of the PIP. Due to the selective charging ink is attracted to image pixels (at locations on the PIP where surface potential was affected by a laser beam), and rejected from background pixels (where the laser has not discharged the surface potential). This latent image is then transferred from the surface of the PIP to an intermediate transfer media (ITM, also known as “blanket”) in what is known as the “first transfer”. The image is then transferred in what is known as “second transfer” from the ITM to the paper by pressing the paper to the ITM by an impressing drum. In order to evaporate solvents present in the ink liquid prior to the encounter with the paper, the surface of the ITM is maintained very hot, and since the ITM and the PIP are firmly pressed against each other during the first transfer, the PIP foil absorbs heat which is to be dissipated before the next printing cycle. Moreover, since the efficiency of the first transfer is not 100%, some ink and imaging oil residues may remain on the surface of the PIP foil, and these residues may therefore inadvertently affect the next printing cycle if not attended to.